Mechanisms behind overshoots in mean cluster size profiles in aggregation-breakup processes

JOURNAL OF COLLOID AND INTERFACE SCIENCE

卷:528

Article

Sadegh-Vaziri, Ramiar¹  Ludwig, Kristin²  Sundmacher, Kai^2,3  Babler, Matthaus U.¹ 

[1] KTH Royal Inst Technol, Dept Chem Engn, SE-10044 Stockholm, Sweden

[2] Max Planck Inst Dynam Complex Tech Syst, Proc Syst Engn, Sandtorstr 1, D-39106 Magdeburg, Germany

[3] Otto von Guericke Univ, Proc Syst Engn, Univ Pl 2, D-39106 Magdeburg, Germany

关键词: Population balance modeling;    Colloidal aggregation;    Shear aggregation;    Aggregate breakup;    Restructuring;    Flocculation;    Fractal aggregates;    Turbulence;   

DOI  :  10.1016/j.jcis.2018.05.064

来源: Elsevier

【 摘 要 】

Aggregation and breakup of small particles in stirred suspensions often shows an overshoot in the time evolution of the mean cluster size: Starting from a suspension of primary particles the mean cluster size first increases before going through a maximum beyond which a slow relaxation sets in. Such behavior was observed in various systems, including polymeric latices, inorganic colloids, asphaltenes, proteins, and, as shown by independent experiments in this work, in the flocculation of microalgae. This work aims at investigating possible mechanism to explain this phenomenon using detailed population balance modeling that incorporates refined rate models for aggregation and breakup of small particles in turbulence. Four mechanisms are considered: (1) restructuring, (2) decay of aggregate strength, (3) deposition of large clusters, and (4) primary particle aggregation where only aggregation events between clusters and primary particles are permitted. We show that all four mechanisms can lead to an overshoot in the mean size profile, while in contrast, aggregation and breakup alone lead to a monotonic, S shaped size evolution profile. In order to distinguish between the different mechanisms simple protocols based on variations of the shear rate during the aggregation-breakup process are proposed. (C) 2018 Elsevier Inc. All rights reserved.

【 授权许可】

Free